KR20060043612A - Method for producing α-alumina powder - Google Patents

Abstract

The present invention provides a method for producing α-alumina powder. The method for producing α-alumina powder

(1) grinding the metal compound having the half height width Ho of the main peak of the XRD pattern to obtain seed crystals having the half height width H of the main peak of the XRD pattern,

(2) mixing the obtained seed crystals with an aluminum compound, and

(3) calcining the mixture

Wherein the ratio of H / Ho is at least 1.06.

 α-alumina powder, seed crystal, aluminum salt, calcined

Description

Production method of α-alumina powder {METHOD FOR PRODUCING AN α-ALUMINA POWDER}

1 shows a method for calculating the half-height width (hereinafter abbreviated as "FWHM") Ho of a metal compound and FWHM H of seed crystals.

2 is a diagram showing an example of a transmission electron micrograph (hereinafter abbreviated as "TEM") of an α-alumina powder.

3 shows an X-ray diffraction (hereinafter abbreviated as "XRD") pattern of a metal compound.

4 shows an XRD pattern of seed crystals used in Example 1;

FIG. 5 is a diagram showing a TEM of α-alumina powder obtained in Example 1. FIG.

6 shows an XRD pattern of seed crystals used in Example 2. FIG.

7 is a diagram showing a TEM of an α-alumina powder obtained in Example 2. FIG.

The present invention relates to a method for producing α-alumina powder having a high α-ratio and a wide BET specific surface area to provide a small amount of necked α-alumina particles.

α-alumina is a kind of aluminum oxide having a corundum structure represented by the chemical formula Al ₂ O ₃ and widely used as a raw material for producing a sintered body such as a translucent tube.

From the viewpoint of improving the strength of the sintered compact, the α-alumina used as a raw material is required to provide a high α-rate, a wide BET specific surface area, and a small amount of necked α-alumina particles.

The present inventors have studied a method for producing α-alumina powder, and as a result, the present invention has been completed.

That is, the present invention

(1) grinding the metal compound having the FWHM (Ho) of the main peak of the XRD pattern to obtain seed crystals having the FWHM (H) of the main peak of the XRD pattern,

(2) mixing the obtained seed crystals with an aluminum compound, and

(3) calcining the mixture

It includes, wherein the ratio of H / Ho provides a method for producing α-alumina powder of 1.06 or more.

The method for preparing α-alumina powder of the present invention comprises the step (1) of grinding the metal compound having the FWHM (Ho) of the main peak of the XRD pattern to obtain seed crystals having the FWHM (H) of the main peak of the XRD pattern. Include.

The metal compound may be advantageous for promoting the phase transformation of the aluminum compound into α-alumina in the calcination step mentioned later. Examples of metal compounds are metal oxides such as α-alumina (Al ₂ O ₃ ), α-iron oxide (Fe ₂ O ₃ ), α-chromium oxide (Cr ₂ O ₃ ); Metal hydroxides such as diaspore (AlOOH), preferably metal oxides, more preferably α-alumina.

Grinding can be carried out in a dry or wet method and a batch-wise or continuous method. Dry grinding is, for example, a ball mill, a vibration mill, a planetary mill, a pin mill, a medium-agitating mill and a jet mill. by using a mill such as mill). In dry grinding, it is desirable to reduce contamination, for which the constituent materials (eg grinding media, vessels, nozzles and liners) that are in contact with the aluminum compound may be alumina, preferably alumina having a purity of at least 99% by weight. It is recommended to use.

Dry grinding may be carried out in the presence of a grinding agent. Examples of grinding agents include alcohols such as ethanol and propanol; Glycols such as propylene glycol, polypropylene glycol, ethylene glycol and polyethylene glycol; Amines such as triethanol amine; Fatty acids such as palmitic acid, stearic acid and oleic acid; Metal alkoxides such as aluminum alkoxides; Carbon materials such as carbon black and graphite. Grinding agents may be used independently or may use 2 or more types together. The amount of the grinding agent is usually about 0.01 part by weight or more, preferably about 0.5 part by weight or more, more preferably about 0.75 part by weight or more, based on 100 parts by weight of the metal compound; And usually about 10 parts by weight or less, preferably about 5 parts by weight or less, and more preferably 2 parts by weight or less.

Wet milling can be carried out by using mills such as, for example, pin mills and medium stirring mills. In wet grinding, it is also desirable to reduce contamination, and for this purpose it is possible to use alumina, preferably alumina having a purity of at least 99% by weight as the constituent material (eg grinding medium, container and liner) in contact with the aluminum compound. It is recommended. Wet grinding is usually carried out in the presence of water. Wet grinding may be carried out in the presence of a dispersant or a surfactant. Examples of dispersants include acids such as nitric acid, hydrochloric acid, sulfuric acid, acetic acid and oxalic acid; Alcohols such as methanol, ethanol, isopropyl alcohol; Aluminum salts such as aluminum nitrate, aluminum chloride, aluminum oxalate and aluminum acetate. Examples of surfactants are anionic surfactants, cationic surfactants, nonionic surfactants and amphoteric surfactants.

In addition, seed crystals obtained by grinding may be classified. By fractionation, at least 50% by weight, preferably at least 70% by weight and more preferably at least 90% by weight of coarse particles (eg particles having a particle diameter of at least about 1 μm) can be removed from the seed crystals.

The seed crystal obtained by the above method usually has a primary particle size of about 0.01 μm or more, preferably about 0.05 μm or more, and usually about 0.5 μm or less. Seed crystals generally have a BET specific surface area of at least about 12 m ² / g, preferably at least about 15 m ² / g, and usually at most about 150 m ² / g.

Grinding is carried out under conditions which change the metal compound having a FWHM of Ho to a metal compound having a FWHM of H, wherein the ratio of H and Ho is at least about 1.06, preferably at least about 1.08, and usually at most about 5, Preferably it is about 4 or less, More preferably, it is about 3 or less. The ratio of H / Ho indicates the degree of grinding and, as shown in FIG. 1, the FWHM (Ho) of the major peak between 45 and 70 degrees in the XRD pattern measured before grinding and the main in the XRD pattern after grinding. Calculated from the FWHM (H) of the peak.

When the metal compound is α-alumina and the X-ray light source is CuK α ray, the displayed H / Ho ratio is FWHM (Ho) of the alumina 116 diffraction peak observed at 2θ of about 57.5 degrees in the XRD pattern before grinding. And FWHM (H) of the alumina 116 diffraction peak in the XRD pattern after grinding.

As for α-iron oxide (Fe ₂ O ₃ ), α-chromium oxide (Cr ₂ O ₃ ) or diaspore (AlOOH), the main peak between 45 and 70 degrees is usually the peak of (116). It is observed at a position close to the position of the α-alumina in the XRD pattern measured using the CuK α ray as the X-ray light source.

The method of the present invention further comprises the step (2) of mixing the obtained seed crystals with an aluminum compound.

The aluminum compound may be a compound which is converted to α-alumina in the calcination step mentioned later, examples of which include aluminum hydroxide, transition alumina, aluminum salts, hydrolysates of aluminum salts, and hydrolysates of aluminum alkoxides.

Aluminum hydroxide may, for example, be crystallized in gibbsite, boehmite, pseudo-boehmite, bayerite, norstrandite, or diaspore. (diaspore), or a crystalline compound that is an amorphous compound.

The transition alumina is, for example, in which the crystal phase is γ, χ, θ, ρ, or κ.

Aluminum salts include, for example, inorganic aluminum salts such as aluminum nitrate, aluminum sulfate, aluminum ammonium sulfate and ammonium hydroxide aluminum hydroxide; Or organic aluminum salts such as aluminum oxalate, aluminum acetate, aluminum stearate, ammonium alum, aluminum lactate and aluminum laurate.

Hydrolysates of aluminum salts are, for example, hydrolyzates of water-soluble aluminum compounds, and examples of hydrolyzates include those obtained by mixing aluminum salts (inorganic aluminum salts, organic aluminum salts) with a base in the presence of water or by hydrolyzing aluminum salts. do. The concentration of aluminum salt in the aqueous solution is usually from about 0.01 mol / L to saturation relative to Al ₂ O ₃ , and the pH is usually from about 0 to about 2. It is preferred that the aluminum salt is completely soluble in water. The aqueous solution of aluminum salt may comprise an organic solvent, which may be evaporated or decomposed in the calcination step mentioned later, examples of which are polar organic solvents such as methanol, ethanol, n-propanol, isopropanol and the like. And nonpolar organic solvents such as carbon tetrachloride, benzene and hexane. The base is a substance that does not contain metal components such as aqueous ammonia solution, ammonia gas, ammonium carbonate, and ammonium bicarbonate. The concentration of the base is at least about 1% by weight and at most about 50% by weight, preferably at most about 25% by weight. Hydrolysis is usually at a pH of at least 3 and preferably at most 5, at most about 60 ^° C., preferably at most about 50 ^° C., more preferably at most about 45 ^° C., above the freezing point of the aqueous solution mentioned above, preferably Preferably at a temperature of about 0 ^° C. or more, for about 1 hour to about 72 hours.

Aluminum alkoxides are, for example, aluminum isopropoxide, aluminum ethoxide, aluminum sec-butoxide and aluminum t-butoxide.

The hydrolyzate of aluminum alkoxide is, for example, a hydrolyzate of aluminum isopropoxide, aluminum ethoxide, aluminum sec-butoxide and aluminum t-butoxide, examples of which are usually 3 or more and preferably 5 or less water obtained by mixing the pH having water with the aluminum alkoxide. Water having a pH of 3 to 5 can be obtained by adding an acid (such as nitric acid) to the water. The aluminum alkoxide may comprise an organic solvent, and such an organic solvent may be one that is evaporated or decomposed in the calcination step described below, and examples thereof include carbon tetrachloride and polar organic solvents such as methanol, ethanol, n-propanol, isopropanol, and the like. Non-polar organic solvents such as benzene and hexane. The hydrolysis is usually at a pH of at least 3 and preferably at most 5 and at a temperature of about 60 ^o C or less, preferably 50 ^o C or less, more preferably about 45 ^o C or less, and usually 0 ^o C or more, about 1 And from about 72 hours to about 72 hours.

The mixture obtained by hydrolysis may usually comprise hydrolyzate and water. Since the hydrolyzate is usually insoluble in water, the mixture may be in the form of a sol or gel, or may comprise precipitation of the hydrolyzate.

The mixing in step (2) comprises, for example, a method of mixing seed crystals with at least one selected from the group consisting of aluminum hydroxide, transition alumina, hydrolysates of aluminum salts, hydrolysates of aluminum alkoxides; (B) mixing seed crystals with an aluminum salt; And method (c) of mixing the seed crystal with the aluminum alkoxide.

The amount of seed crystal is based on 100 parts by weight based on the total amount of the seed crystal and at least one aluminum compound selected from the group consisting of aluminum hydroxide, transition alumina, hydrolyzate of aluminum salt, hydrolyzate of aluminum alkoxide, aluminum salt and aluminum alkoxide. , Usually about 1 part by weight or more, preferably about 2 parts by weight or more, more preferably about 4 parts by weight or more, and usually 50 parts by weight or less, preferably about 40 parts by weight or less, and more preferably 25 parts by weight. It is as follows.

In method (a) or method (b), the mixing is done in the presence of water. The amount of water is usually about 150 parts by weight or more, preferably about 200 parts by weight or more, and usually about 1000 parts by weight or less, preferably about 500 parts by weight or less based on 100 parts by weight of the total amount of the seed crystal and the aluminum compound.

In the method (b) or the method (c), it is preferable to satisfy the following expression (1).

W ≥ 350 / S

At this time, W (Al ₂ O ₃ , Fe ₂ O ₃ , Cr ₂ O ₃ Parts by weight of the same metal oxide) is the amount of seed crystals based on 100 parts by weight of Al ₂ O _{3 based} on the total amount of seed crystals and aluminum compounds, and S (m ² / g) is the BET specific surface area of the seed crystals. to be.

It is more preferable to satisfy the following expression (2).

7500 / S ≥ W ≥ 400 / S

The mixture of seed crystals and aluminum salts or aluminum alkoxides may further be hydrolyzed. Hydrolysis is usually at a pH of at least 3 and preferably at most 5 and at a temperature of about 60 ^o C or less, preferably 50 ^o C or less, more preferably about 45 ^o C or less, and usually 0 ^o C or more, about 1 It can be done for hours to 72 hours.

The mixture obtained can further be dried. Drying can usually be carried out using a freeze dryer, vacuum dryer or the like at a temperature of about 100 ^° C. or lower.

In addition, the obtained mixture may be heated. The heating can be done at a temperature below the temperature at which the aluminum compound is converted to α-alumina. The heating temperature is usually higher than about 100 ^° C., preferably higher than about 300 ^° C., and usually lower than about 600 ^° C.

If the heating is done using a furnace, such as the furnace used in Example 1, equipped with an inlet for injecting the mixture and gas and an outlet for exiting the mixture and gas, the heating conditions are It is desirable to satisfy.

Where x (g / sec) is the rate of injection of the mixture containing the hydrolyzate of the aluminum compound,

V ₂ (standard-m ³ / sec) shows the rate of injection of inert gas,

P (Pa) is the atmospheric pressure in the furnace,

A (m ² / g) is the open surface area in the outlet,

n (mol / g) is the molar amount of gas generated from 1 g of the mixture,

R is the gas constant (= 8.31 Pa · m ³ / mol / K),

T (K) is the outlet temperature in the furnace,

To (K) is the ambient temperature outside the furnace, and

ρ (m / sec) represents the flow rate of the gas ejected from the outlet.

The process of the invention further comprises the step (3) of calcining the mixture obtained above.

The calcination stages include tubular furnaces, box-type furnaces, tunnel furnaces, far infrared furnaces, microwave furnaces, shaft furnaces, reflection furnaces, rotary furnaces and roller-hearth furnaces. It can be advantageously carried out using a device. Calcination can be carried out batchwise or continuously. It may also be carried out in a stationary or flow mode.

The calcination temperature is not lower than the temperature at which the aluminum compound is converted to α-alumina and is usually at least 600 ^o C, preferably at least about 700 ^o C, and usually at most about 1000 ^o C and preferably at most about 950 ^o C. . The calcination time is usually 10 minutes or more, preferably about 30 minutes or more, and usually about 24 hours or less, preferably about 10 hours or less.

Calcination is usually done in air or under an inert gas such as N ₂ or Ar. Calcination may also be done under air with a controlled partial pressure of steam, for example under air with a steam partial pressure of 600 Pa or less.

The α-alumina powder obtained can be milled. Grinding can be carried out using, for example, medium pulverizers such as vibratory mills and ball mills, or pneumatic pulverizers such as jet mills. Furthermore, α-alumina powder may be classified.

The α-alumina powder obtained by the method of the present invention has an average particle diameter of about 0.01 μm or more, preferably about 0.05 μm or more, and usually about 0.1 μm or less, preferably about 0.09 μm or less, and the α-ratio is At least about 90%, preferably at least about 95%, and the BET specific surface area is at least about 15 m ² / g, preferably at least about 17 m ² / g, and at most about 50 m ² / g.

Example

The invention is further illustrated and described by the following examples, which should not be construed as limiting the scope of the invention.

The properties of α-alumina and seed crystals were measured as follows.

(1) α-ratio

peak intensity I _{25 .6} at 2θ = 25.6 ^o corresponding to the peak intensity of α-alumina 012 and 2θ = 46 corresponding to the peak intensity of alumina different from α-alumina _. ^From the diffraction spectrum measured under the condition of 'irradiator: CuK α light, 40 kV x 20 mA, monochromator: graphite' using the peak intensity I ₄₆ at ^o , the following equation (4) Calculated accordingly.

α-ratio = I _{25 .6} / (I _{25 .6} + I ₄₆ ) x 100 (%)

(2) Average primary particle size

From the transmission electron micrograph of the α-alumina powder, the maximum diameter along the constant direction of each initial particle of any 20 or more particles was measured, and the average value of the measurements was calculated.

(3) BET specific surface area

It measured by the nitrogen adsorption method using the specific surface area analyzer (trade name "FLOWSORB II 2300" by Shimadzu Corporation).

(4) degree of pulverization

Seed crystal (α-alumina) XRD spectra before and after the grinding operation were measured using an X-ray diffractometer. The half-height widths of phase 116, ie Ho 116 (before grinding) and H 116 (after grinding), were obtained as XRD spectra and calculated using Equation 5.

Grinding Degree = H (116) / Ho (116)

(5) degree of necking

Between 20 or more particles in transmission electron micrographs taken of α-alumina powder, the proportion of those in which two or more initial particles were in the form of agglomerates was measured. As shown in FIG. 2, the measuring method can be explained by the following example.

In the drawing:

Initial particles not in lump form: 18

2 initial particles in lump form: 1

Initial particles in three-lump form: 1

In this case, the necking degree is 10%. [= 2 / (18 + 1 + 1)]

Example 1

[Production of Metal Compound (α-alumina)]

Hydrolysis and pre-calcination of aluminum isopropoxide gave transition alumina containing θ phase and 3 wt% of α phase as the main crystal phase, and the transition alumina was ground with a jet mill to give a bulk density of 0.21 g / A powder of cm ³ was obtained.

The powder obtained was calcined under the following conditions in a furnace filled with air having a dew point of -15 ^° C. (partial vapor pressure of 165 Pa).

Method: continuous injection and discharge

Average retention time: 3 hours

Maximum temperature: 1170 ^o C

Thus, α-alumina having a half-height width of Ho ₍₁₁₆₎ and a BET specific surface area of 14 m ³ / g was obtained.

 The XRD pattern of α-alumina is shown in FIG. 3.

[Pulverization of α-alumina]

100 parts by weight of α-alumina and 1 part by weight of propylene glycol were filled into a vibration mill as a grinding agent, and the α-alumina powder was ground under the following conditions.

Medium: alumina beads with a diameter of 15 mm

Residence time: 12 hours

As a result, seed crystals having a half-height width of H ₍₁₁₆₎ , a BET specific surface area of 17.2 m ³ / g and an average particle diameter of 0.1 μm were obtained. The XRD pattern of seed crystals is shown in FIG. 4. In this example, the degree of grinding of H ₁₁₆ / Ho ₁₁₆ is 1.1.

Preparation of Seed Crystal Slurry

37.5 g of seed crystals were dispersed in 150 g of 0.01 mol / L aluminum nitrate solution to obtain a slurry. The slurry and 700 g of alumina beads having a diameter of 2 mm were filled into a plastic container having an internal volume of 1 L, and stirred. The contents of the container were taken out, and the alumina beads were filtered off to obtain a seed crystal slurry.

[Mixing of Seed Crystal and Aluminum Compound]

750.26 g (2 mol) of aluminum nitrate hexahydrate (Al (NO ₃ ) ₃ · 9H ₂ O) (manufactured by Kansai Catalyst Co., Ltd., reagent grade, appearance: powder) in 1555.7 g of aluminum nitrate solution Got. To the aluminum nitrate solution was added 218.6 g (43.4 g of Al ₂ O ₃ ) seed crystals mentioned above and a 25% aqueous ammonium solution (manufactured by Wako Pure Chemical Industries. Ltd., special reagent grade) at room temperature with stirring. g (ie 85.12 g (5 mol) to NH ₃ ) was added at a feed rate of 32 g / min using a micro rotary pump to give a mixture. The pH of the obtained mixture was 3.9. The mixture was left at room temperature, dried at 60 ^° C., and ground using mortar to obtain a mixed powder. The mixed powder contained 85 g (for Al ₂ O ₃ ) amorphous alumina, 390 g (for NH ₄ NO ₃ ) ammonium nitrate, 71 g (for Al (NO ₃ ) ₃ ) aluminum nitrate and seed crystals. The amount of seed crystals based on Al ₂ O ₃ was 30 parts by weight per 100 parts by weight of the mixed powder.

[calcination]

The mixed powder was pre-calcined using a rotary furnace (manufactured by Takasago Industry Co., Ltd.) with an internal volume of 79L under the following conditions.

Method: continuous injection, continuous discharge

Injection rate of powder: 20 g / min

Furnace temperature

Inlet port: 490 ^o C

Outlet: 390 ^o C

Pressure: 0.1MPa

Rate of gas injection: 10 standard liquid nitrogen (N ₂ ) / min

Flow rate of exhaust gas: 2.8 m / sec

Rotating Speed of Rotary Furnace: 2 rpm

Based on 1 g of mixed powder, the mixed powder produced 34.7 × 10 ⁻³ mol of gas. The powder discharged from the rotary furnace was placed in a crucible made of alumina, and the crucible was placed in the furnace. The powder was then heated to 920 ^° C. at a rate of temperature rise of 300 ^° C. per hour, and calcined by holding at 920 ^° C. for 3 hours. The properties of the α-alumina powder are shown in Table 1. The TEM of the obtained α-alumina powder is shown in FIG. 5.

Example 2

The seed crystal slurry obtained in [Preparation of seed crystal slurry] in Example 1 was centrifuged for 40 minutes at a rotational speed of 4000 rpm to obtain fine α-alumina seed crystals having a BET specific surface area of 38.1 m ² / g. The supernatant containing weight% was obtained. The XRD pattern of seed crystals is shown in FIG. 6. In this example, the degree of grinding of H ₁₁₆ / Ho ₁₁₆ is 1.38.

375.13 g (1 mol) of aluminum nitrate hexahydrate (Al (NO ₃ ) ₃ · 9H ₂ O) (manufactured by Kansai Catalyst Co., Ltd., reagent grade, appearance: powder) in 777.87 g of water in aluminum nitrate solution Got. To the aluminum nitrate solution was added 171.7 g of the above-mentioned seed crystals (5.67 g for Al ₂ O ₃ ) and a 25% ammonium aqueous solution (manufactured by Wako Pure Chemical Industries. Ltd., special reagent grade) at room temperature with stirring. (Ie 40.422 g (5 mol) to NH ₃ ) was added at a feed rate of 32 g / min using a micro rotary pump to give a mixture. The pH of the obtained mixture was 3.9. The mixture was left at room temperature, dried at 60 ^° C., and ground using mortar to obtain a mixed powder. The mixed powder contained 85 g (for Al ₂ O ₃ ) amorphous alumina, 390 g (for NH ₄ NO ₃ ) ammonium nitrate, 71 g (for Al (NO ₃ ) ₃ ) aluminum nitrate and seed crystals. The amount of seed crystals based on Al ₂ O ₃ was 10 parts by weight per 100 parts by weight of the mixed powder.

The same operation as in [calcination] of Example 1 was carried out except that the calcination temperature was changed to 900 ^° C. The properties of the α-alumina powder are shown in Table 1. The TEM of the obtained α-alumina powder is shown in FIG. 7.

Table 1. Properties of α-alumina powder Example 1 Example 2 α-ratio (%) 98 98 BET specific surface area (m ³ / g) 16.9 18.8 Average primary particle size (μm) 57 74 Necking degree (%) 8 17

The α-alumina powder, as described above, has a high α-ratio, a wide BET specific surface area, and has a small amount of necked particles, which is useful as a raw material for producing α-alumina sintered body having high strength. Do. The resulting α-alumina sintered body can be used for cutting tools, bioceramics, low-resistance routing pattern ceramics (e.g. copper pattern over alumina ceramics), and those requiring high strength such as bulletproof boards. It is suitable as a component part. The α-alumina sintered body is a semiconductor filter such as a wafer handler, an electronic component such as an oxygen sensing device, a semi-transparent tube such as a sodium lamp or a metal halogen lamp, or a ceramic filter due to chemical stability such as excellent corrosion resistance. It is used as part of the mechanism to be manufactured. Ceramic filters include the removal of solids contained in exhaust gases, the filtration of aluminum melts, the filtration of beverages such as beer, or the selective generation of gases or CO, CO ₂ , N ₂ , O ₂ , H ₂ gases generated during petroleum treatment. Used for transmission The α-alumina powder may be used as a sintering agent for ceramics such as thermally conductive ceramics (eg AlN), YAG, or phosphorescent materials.

Furthermore, α-alumina powder It is added to the application layer of the magnetic medium in the form of application to improve the head purification properties and friction resistance, It may be used as an additive for toner or resin filler. In addition, α-alumina powder may be used as an additive in cosmetics or brake linings.

In addition, α-alumina powder is also used as an abrasive material. For example, a slurry obtained by dispersing α-alumina powder in a medium such as water is suitable for polishing in semiconductor CMP and polishing of hard disk plates. An abrasive tape obtained by coating α-alumina particles on the tape surface is suitable for precise polishing of a hard disk or a magnetic head.

Claims (14)

(1) grinding the metal compound having the half height width Ho of the main peak of the XRD pattern to obtain seed crystals having the half height width H of the main peak of the XRD pattern, (2) mixing the obtained seed crystals with an aluminum compound, and (3) calcining the mixture  To include, wherein the ratio of H / Ho is 1.06 or more method of producing alumina powder. The method for producing α-alumina powder according to claim 1, wherein the metal compound is at least one selected from the group consisting of metal oxides and metal hydroxides. The method for producing α-alumina powder according to claim 2, wherein the metal compound is at least one selected from the group consisting of α-Al ₂ O ₃ , α-Fe ₂ O ₃ , α-Cr ₂ O _3, and diaspores. . The method for producing α-alumina powder according to claim 1, wherein the ratio of H / Ho is 5 or less. The method for producing α-alumina powder according to claim 1, wherein the aluminum compound is at least one selected from the group consisting of aluminum hydroxide, transition alumina, aluminum salts, hydrolysates of aluminum salts, hydrolyzates of aluminum alkoxides and aluminum alkoxides. The method for producing α-alumina powder according to claim 5, wherein the aluminum compound is at least one member selected from the group consisting of aluminum salts and aluminum alkoxides. The method according to claim 6, wherein the amount of seed crystal W (parts by weight based on 100 parts by weight of Al ₂ O ₃ based on the total amount of seed crystals) and the BET specific surface area S (m ² / g) of the seed crystals are as follows. Method for producing α-alumina powder satisfying the equation. W ≥ 350 / S The method for producing α-alumina powder according to claim 1, wherein the aluminum compound is at least one selected from the group consisting of aluminum hydroxide, transition alumina, aluminum salt, hydrolyzate of aluminum salt and hydrolyzate of aluminum alkoxide. The process for producing α-alumina powder according to claim 8, wherein the mixing step is carried out in the presence of water. 10. The method of claim 9, wherein the amount of water is from about 150 to about 1000 parts by weight based on 100 parts by weight of the total amount of the aluminum compound and the seed crystals. The method for producing α-alumina powder according to claim 5, wherein the aluminum compound is an aluminum salt. 12. The method of claim 11, further comprising hydrolyzing the aluminum compound by mixing a base with the mixture of step (2). The process for producing α-alumina powder according to claim 12, wherein the hydrolysis is performed at a pH of 3 or more. The process for producing α-alumina powder according to claim 13, wherein the hydrolysis is performed at a pH of 3 to 5.

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